Add __INTRODUCED_IN hack to complex test.

complex_test.cpp is compiled with both bionic and glibc, so when
__INTRODUCED_IN starts being used in <complex.h>, we'll need this to
keep it building.

Bug: http://b/28178111
Change-Id: I6431111be35288cad72e9c23ca8599f548b6d906
diff --git a/tests/complex_test.cpp b/tests/complex_test.cpp
index 3b8e682..8ddd28b 100644
--- a/tests/complex_test.cpp
+++ b/tests/complex_test.cpp
@@ -16,6 +16,13 @@
 
 #include <gtest/gtest.h>
 
+// This file is compiled against both glibc and bionic, and our complex.h
+// depends on bionic-specific macros, so hack around that.
+#include <sys/cdefs.h>
+#if !defined(__INTRODUCED_IN)
+#define __INTRODUCED_IN(x)
+#endif
+
 // libc++ actively gets in the way of including <complex.h> from C++, so we
 // have to be naughty.
 #include <../libc/include/complex.h>